1. Field of the Invention
The present invention relates to a sheet material cutting unit for cutting a long length of a printed sheet material at a desired position and to a printing device provided with the sheet material cutting unit.
2. Related Background Art
Conventionally, as a sheet material cutting device, one for cutting a sheet material placed between a fixed blade and a movable blade by reciprocating the movable blade with respect to the fixed blade and sliding the two blades with respect to each other, “a cut-through type” sheet material cutting device, is widely known.
Since such a sheet material cutting device can cut a sheet material with a simple drive, it is suitable to be mounted on a small printer device provided for a cash register or an ATM which issues a receipt. A sheet material cutting device described in Patent Document 1 is one such the sheet material cutting unit.
Here, operation of a conventional sheet material cutting unit of a cut-through type is described with reference to FIG. 6, FIG. 7 A, FIG. 7 B, FIG. 7 C, FIG. 7 D, FIG. 7 E, FIG. 7 F, and FIG. 8. FIG. 6 is a sectional view illustrating a thermal printer 101 provided with a conventional sheet cutting unit. FIG. 7A to FIG. 7F are a view illustrating operation of the conventional sheet material cutting unit. FIG. 8 is an enlarged view of a main part during conventional cutting of a sheet material.
As illustrated in FIG. 6, a conventional thermal printer is provided with a sheet material cutting unit 105 above a printing portion 104 having a thermal head 102 for printing and a platen roller 103. A sheet material S to be printed such as a roll of thermal paper is transferred from a lower part of the printer, and when it passes between the thermal head 102 for printing and the platen roller 103, printing is carried out. The printed sheet material S is sent to the sheet material cutting unit 105 to be cut to a desired length.
The sheet material cutting unit 105 is provided with a fixed blade unit 106 and a movable blade unit 107 placed to be opposed to the fixed blade unit 106. The fixed blade unit 106 is formed of a fixed blade holder 109, a fixed blade 108 fixed by the fixed blade holder 109, a supporting portion 110 provided in the fixed blade holder 109 for rotatably supporting an end opposite to a cutting edge of the fixed blade 108, and a spring member 111 provided between the fixed blade 108 and the fixed blade holder 109 for biasing upward the cutting edge of the fixed blade 108.
On the other hand, the movable blade unit 107 is formed of a movable blade 112, a movable blade holder 113, and a slide mechanism capable of horizontally sliding the movable blade 112 with respect to the fixed blade 108. The movable blade holder 113 is a plate-like member made of a plastic member or the like, and functions as a guide for protecting the movable blade 112 against direct contact with a housing and for sliding the movable blade 112 straight. Further, the movable blade 112 has an outer appearance where its cutting edge is substantially V-shaped or formed in a slanting direction, and is reciprocated horizontally with respect to the fixed blade 108 by the slide mechanism.
During standby before cutting, an upper surface of the fixed blade 108 is positioned above a lower surface of the movable blade 112 with the biasing force of the spring member 111. Therefore, when the movable blade 112 is moved toward the fixed blade 108 by the slide mechanism and an attracting portion 114 formed at the tip of the movable blade 112 runs onto and intersects the fixed blade 108, the fixed blade 108 is pressed down to a horizontal position of the movable blade 112 against the biasing force of the spring member 111. Thus, contact pressure which is equal to the reaction force of the spring member 111 acts between the cutting edges of the movable blade 112 and the fixed blade 108. By moving the movable blade 112 on the upper surface of the fixed blade 108 with this state maintained, the movable blade 112 and the fixed blade 108 slide on each other with the contact pressure and the sheet material S which is interposed between the blades is cut.
Here, as illustrated by vertical arrows in FIG. 8, when the sheet material is cut, the sheet material S applies side pressure to the movable blade 112 and the fixed blade 108 such that the space between the blades is widened. Therefore, in order to cut the sheet material S, it is necessary that the contact pressure between the movable blade 112 and the fixed blade 108 is higher than this side pressure. However, if the contact pressure is too high, frictional load applied to the fixed blade 108 and the movable blade 112 is increased, and thus, a problem is caused that the capacity of a motor for driving the movable blade 112 has to be increased further than necessary.
Further, the larger the slant angle of the sheet material S is, the higher the side pressure becomes. Therefore, when the blades are worn out and blunted such that the sheet material S tends to fall in the sliding direction of the movable blade 112, the side pressure applied from the sheet material S is increased. When the side pressure becomes higher than the contact pressure, the posture in the cutting is not stable, poor cutting is caused, and, as illustrated in FIG. 7C, the sheet material S is caught between the fixed blade 108 and the movable blade 112. After that, the movable blade 112 returns to its initial position as illustrated in FIGS. 7D to 7F, but the sheet material remains uncut.
In order to solve such problems, conventionally, two possible ways have been proposed:
(1) suppress the wear of the blades; and
(2) is to form an outlet in the housing such that the sheet material becomes more difficult to fall.
However, in the case of (1), though methods such as increasing the hardness of the material of the blades, increasing the robustness of the blades by quenching the blades themselves, and performing surface hardening process such as coating can be considered, these methods have a problem that the cost is increased.
Further, in the case of proposal (2), although the falling of the sheet material S can also be prevented by narrowing the width of the outlet in the housing of the printing device body to thereby support the sheet material S, there is also a problem that, if the width of the outlet is decreased too much, the sheet material tends to jam near the outlet when the sheet material is transferred. Therefore, in order that both the falling of the sheet material and the jam of the sheet material are reduced, the width and the angle of the sheet material outlet in the housing must be limited, to restrict thereby restricting the design flexibility of the housing.